Implantable shunt systems are used in the medical field for directing body fluid from one region to another. To treat patients with hydrocephalus, fluid shunt systems can be used to remove and discharge excess cerebrospinal fluid (“CSF”). Draining the excess fluid relieves elevated intracranial pressure. Generally, valve mechanisms control or regulate the flow rate of fluid through the shunt system. The valve mechanisms may permit fluid flow only when fluid pressure reaches a certain threshold level. The fluid flow rate is proportional to the pressure at the valve mechanism and thus, for a pressure that is only slightly higher than the threshold or opening pressure, the flow rate is relatively low. As the fluid pressure increases, the flow rate through the shunt system increases. At pressures that are significantly higher than the threshold pressure, a maximum flow rate for the system is reached. Fluid flow normally continues until the intracranial pressure has been reduced to a level less than the threshold pressure.
The threshold or opening pressure that allows fluid flow through a shunt system often needs to be adjusted. A medical professional may initially select a relatively low opening pressure to trigger fluid flow. Over time, the initial opening pressure may require adjustment, for example in a situation where excess fluid flow creates an undesirable overdrainage condition, which may necessitate an increase in the opening pressure to produce a fluid flow rate that is balanced. Some valve systems allow a medical professional to non-invasively customize an implanted valve mechanism's opening pressure for a particular patient.
A Hakim valve is a commonly used differential pressure valve having selectable precise opening pressures. Current practice may require that an x-ray be taken to verify a new setting after each valve adjustment. Conventional approaches for determining valve position can have undesirable complications. As an example, when magnetic fields are used for verifying valve position, metallic equipment within a clinical environment may interfere with the accuracy of information obtained through the use of these magnetic forces, which can lead to inaccurate readings.
U.S. Pat. No. 6,685,638 describes an apparatus for acoustically monitoring the position of a Hakim shunt. In some circumstances, it may be difficult to accurately determine valve position using acoustics. For example, environmental factors such as the presence of ambient sound may in some cases effectively limit the signal-to-noise ratio of an acoustic reading. Also, it may be challenging to clearly identify acoustic position signals across all patients because the thickness of subcutaneous layers of tissue can vary from patient to patient.
It is with respect to these and other considerations that the various example implementations described below are presented.